Re: ACPI/i915: Cannot configure display brightness on Dell Latitude E6440

Rafael J. Wysocki
2014-09-25T19:58:48Z

On Thursday, September 25, 2014 11:15:35 AM Aaron Lu wrote:
> Hi Hans,
>
> Thanks for following up and explaining the situation to Pali.
>
> On 09/25/2014 02:21 AM, Pali Rohár wrote:
> > On Wednesday 24 September 2014 16:34:21 Hans de Goede wrote:
> >> Ok, so the dell-laptop interface is just an obsolete wrapper
> >> around the i915 opregion code, which shows that the right
> >> interface to use is the i915 one, which we do if you don't
> >> specify any kernel commandline parameters, case closed.
> >>
> >> Regards,
> >>
> >> Hans
> >
> > Nope, its not closed.
> >
> > Still i915 interface has problem with setting backlight. It
> > exports lot of levels which turning display off. Which breaking
> > exiting applications for configuring display brightness. This is
> > still big regression as black screen is not want people want to
> > see.
> >
> > Driver dell-laptop has exported only few - not thousands level
> > (which is insane) and only usefull levels (not lot of levels
> > which turn display off).
> >
> > So for this reason using i915 backlight interface is not possible
> > and also Dell (for E6440) set kernel param acpi_backlight=vendor
> > to use dell_laptop module for controlling brightness.
> >
> > On my laptop E6440 is better for using dell-laptop and not acpi
> > or i915.
>
> Hi Pali,
>
> Please test this patch:
>
> diff --git a/drivers/gpu/drm/i915/intel_opregion.c b/drivers/gpu/drm/i915/intel_opregion.c
> index ca52ad2ae7d1..15534345bd57 100644
> --- a/drivers/gpu/drm/i915/intel_opregion.c
> +++ b/drivers/gpu/drm/i915/intel_opregion.c
> @@ -396,6 +396,24 @@ int intel_opregion_notify_adapter(struct drm_device *dev, pci_power_t state)
> return -EINVAL;
> }
>
> +/*
> + * Some of the Thinkpads' firmware will issue a backlight change operation
> + * region request unconditionally on AC plug/unplug, this is undesirable and
> + * should be ignored. Then there is a Dell laptop whose vendor backlight
> + * interface also makes use of operation region request to change backlight
> + * level and we have to keep it work. The rule used here is: if the vendor
> + * backlight interface is not in use and the ACPI backlight interface is
> + * broken, we ignore the requests; oterwise, we keep processing them.
> + */
> +static bool should_ignore_backlight_request(void)
> +{
> + if (acpi_video_backlight_support() &&
> + !acpi_video_verify_backlight_support())
> + return true;
> +
> + return false;
> +}

Well, what about

return acpi_video_backlight_support() && !acpi_video_verify_backlight_support();

?

> +
> static u32 asle_set_backlight(struct drm_device *dev, u32 bclp)
> {
> struct drm_i915_private *dev_priv = dev->dev_private;
> @@ -404,11 +422,7 @@ static u32 asle_set_backlight(struct drm_device *dev, u32 bclp)
>
> DRM_DEBUG_DRIVER("bclp = 0x%08x\n", bclp);
>
> - /*
> - * If the acpi_video interface is not supposed to be used, don't
> - * bother processing backlight level change requests from firmware.
> - */
> - if (!acpi_video_verify_backlight_support()) {
> + if (should_ignore_backlight_request()) {
> DRM_DEBUG_KMS("opregion backlight request ignored\n");
> return 0;
> }
> --
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--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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